title: Lovastatin-induced apoptosis is mediated by activating transcription factor 3 and enhanced in combination with salubrinal.
abstract: We have previously demonstrated the ability of lovastatin, a potent inhibitor of mevalonate synthesis, to induce tumor-specific apoptosis. The apoptotic effects of lovastatin were regulated in part by the integrated stress response (ISR) that regulates cellular responses to a wide variety of stress inducers. A key regulator of the ISR apoptotic response is activating transcription factor 3 (ATF3) and its target gene CHOP/GADD153. In our study, we demonstrate that in multiple lovastatin-resistant clones of the squamous cell carcinoma (SCC) cell line SCC9, lovastatin treatment (1-25 μM, 24 hr) in contrast to the parental line failed to significantly induce ATF3 expression. Furthermore, the SCC-derived cell lines SCC25 and HeLa that are sensitive to lovastatin-induced apoptosis also preferentially induce ATF3 expression compared to resistant breast (MCF-7) and prostate carcinoma (PC3)-derived cell lines. In HeLa cells shRNA targeting ATF3 expression as well as in ATF3-deficient murine embryonic fibroblasts, lovastatin-induced cytotoxicity and apoptosis were attenuated. In ex vivo HNSCC tumors, lovastatin also induced ATF3 mRNA expression in two of four tumors evaluated. Salubrinal, an agent that can sustain the activity of a key regulator of the ISR eIF2α, further increased the expression of ATF3 and demonstrated synergistic cytotoxicity in combination with lovastatin in SCC cells. Taken together, our results demonstrate preferential induction of ATF3 in lovastatin-sensitive tumor-derived cell lines that regulate lovastatin-induced apoptosis. Importantly, combining lovastatin with salubrinal enhanced ATF3 expression and induced synergistic cytotoxicity in SCC cells.
authors.affiliation: Centre for Cancer Therapeutics, Ottawa Hospital Research Institute, Ottawa, ON, Canada; Faculty of Medicine and the Department of Biochemistry, University of Ottawa, Ottawa, ON, Canada.
authors.forename: Nima
authors.initials: N
authors.lastname: Niknejad
authors.forename: Ivan
authors.initials: I
authors.lastname: Gorn-Hondermann
authors.forename: Laurie
authors.initials: L
authors.lastname: Ma
authors.forename: Stephanie
authors.initials: S
authors.lastname: Zahr
authors.forename: Stephanie
authors.initials: S
authors.lastname: Johnson-Obeseki
authors.forename: Martin
authors.initials: M
authors.lastname: Corsten
authors.forename: Jim
authors.initials: J
authors.lastname: Dimitroulakos
mesh_terms: D051700:Activating Transcription Factor 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002934:Cinnamates / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004357:Drug Synergism; D004622:Embryo, Mammalian / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000235:genetics / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005434:Flow Cytometry; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000494:pharmacology; D007124:Immunoenzyme Techniques; D008148:Lovastatin / Q000494:pharmacology*; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: C490449:ATF3 protein, human; D051700:Activating Transcription Factor 3; D002934:Cinnamates; D015852:Eukaryotic Initiation Factor-2; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C496827:salubrinal; D008148:Lovastatin; D013890:Thiourea
keywords: activating transcription factor 3; integrated stress response; lovastatin; salubrinal